The present invention relates generally to projection televisions, and more particularly to a cathode ray tube coupler with grounding ribbs to provide electrical grounding and reduce picture abnormalities.
Projection televisions (PTV""s) are well known. A projection TV CRT typically has a flat front glass faceplate, a die-case aluminum coupler and a projection lens assembly for correcting the curvature of an image field. An image displayed on the front glass plate of the projection TV CRT is projected through the coupler and the lens onto a screen.
Rear projection type television receivers are very popular due to the large display screens that are available without the need for special installations and/or large viewing areas. In such receivers, the CRTs project the image onto a mirror, with the image being reflected (and magnified) onto the viewing screen.
In general, a projection television set includes three color cathode ray tubes (CRTs), corresponding to the primary colors, red, green and blue. A plurality of lens elements make up the projection lens assembly that magnifies the image appearing on the CRT faceplate and projects it onto a viewing screen. The CRT-to-lens coupler is utilized to couple the projection lens assembly to the faceplate of the CRT.
A typical coupler is provided with a circular opening in its central portion to receive a lens and side walls defining a rectangular space behind the circular opening, namely on the side of the projection CRT with respect to the circular opening. The lens is held in place by the coupler.
Each of the three CRTs in a projection television is typically operated at maximum power so as to maximize the intensity and to produce maximum light output at the faceplate. This, together with the fact that each of the CRTs is located within the projection television enclosure, tends to generate considerable heat. The lens system is therefore exposed to the elevated temperatures, causing thermally induced expansion of the components in the system (i.e., the focus of the lens system will change as the ambient temperature increases) leading to a variety of distortions.
Modern consumer rear-screen projection televisions typically utilize liquid coupling of the projection optics to the CRT faceplates to enhance contrast and to avoid localized hot spots on the CRT which may result in CRT failure. The space sealed by the projection TV CRT, the lens and the side walls is filled with a cooling liquid to cool the front glass plate and to couple the front glass plate and the lens optically. The coupling of the optics and the CRT is accomplished by way of the metal coupler (die cast or stamped aluminum) which has a durable surface. The coupler is often coated with a nonreflective dark matte finish (e.g. black paint), so as to (1) improve contrast by reducing reflections, and (2) prevent the aluminum casting from corroding.
Specifically, referring now to FIG. 1, a cross-sectional view of a conventional CRT unit 1 for use in a projection television CRT system is shown. CRT unit 1 comprises CRT body 2 with front surface 2A, a die cast coupler 3 with opening portion 4 and lens 5. Cooling liquid 6 is filled into the space defined by panel front surface 2A, coupler 3 and lens 5.
Focusing specifically on the coupler 3, FIG. 2 provides a more detailed perspective view of coupler 3 as seen from the front side thereof, illustrating through holes 23 provided on each of the four corners of flange portion 3B to mount the coupler to CRT rails so as to correctly position the CRT within the television chassis.
However, a problem exists in that in all of the various known coupler systems, a static charge is produced on the glass and also on the coupler itself. As the coupler has a floating ground, i.e., it is not tied to any part of the structure or referenced to any other potential, the static charge of the coupler causes intermittent picture abnormalities.
Accordingly, it would be desirable to provide a CRT coupler that does not have a floating ground, but rather is electrically grounded to the chassis of the television itself, thereby eliminating any picture abnormalities created by the build up of static charge on the coupler. Any improvement of the conventional coupler systems should also be inexpensively manufactured, maintain excellent optical and mechanical coupling characteristics and continue to allow the coupler to be easily installed and removed from the assembly.
In view of the foregoing, it is an object of the present invention to provide a commercially usable metal coupler, for coupling a projection lens to a cathode ray tube, that is grounded to the projection television set.
In accordance with the present invention, a CRT coupler for coupling a projection lens to a cathode ray tube consists of a metallic plate having a first side and a second side, the first side for mounting to the faceplate of the cathode ray tube in a fluid tight relationship, and the second side for mounting to a lens plate. The metallic plate is covered with a non-reflective coating and has at least one through hole for mounting to CRT rails. A plurality of ribbs protrude from the second side of the metallic plate at at least one of the at least one through holes and the ribbs surround the through hole. Upon mounting of a fastening device in the through hole, the fastening device comes into contact with a top surface of the ribbs and the non-reflective coating is removed from the ribbs, thereby forming a ground connection for the coupler.
In one embodiment, the metallic plate has four corners and has a through hole at each of the four corners for mounting to CRT rails. The plurality of ribbs may surround only one of the four through holes, or may surround more than one of the four through holes.
In another embodiment grounding ribbs are integral to the coupler and in yet another embodiment the coupler is covered with a dark matte finish. The fastening device may be a screw and a pair of leaf springs may be used to mount the faceplate of the CRT to the first side of the coupler.
In a further embodiment of the invention, a projection television assembly includes a CRT having a faceplate at an end of the CRT on which an image is displayed, a coupler having a first side and a second side, the first side fixed to the faceplate of the CRT and a lens having a lens plate fixed to the second side of the coupler. The coupler is covered with a non-reflective coating and has at least one through hole for mounting to CRT rails, and a plurality of ribbs, surrounding at least one of the through holes, protrude from the second side of the coupler. Upon mounting of a fastening device in the through hole, the fastening device comes into contact with a top surface of the ribbs and the non-reflective coating is removed from the ribbs, thereby forming a ground connection for the coupler to the projection television assembly.